Ultra high frequency circuit and method



Nov. 2, i948.

W. W. HANSEN Ef AL.

2,452,566 ULTRA HIGH FREQUENCY CIRCUIT AND METHOD Original Filed Aug'. 21. 1943 26a v v f 275 ff N .f-Hzf,l ,L /75k 16471.22*

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ATTORNEY Patented Nov. 2, 1948 UNITD sTAT Es PATENT orner. l

ULTRA HIGH FREQUENCY. CIRCUIT AND METHOD William W. Hansen and John R. Woodyard, Garden City, N. Y., assignors to The Sperry Corporation, a corporation of Delaware Original application August 21, 1943, Serial No.

499,562. Dividedrand this application December 23, 1944, Serial No. 569,516

pending application Serial No. 426,986. led January 16, 1942, in the names of William W. Hansen,

Russell H. Varian, John R. Woodyard, and Ed-' ward L. Ginzton.

In systems of the present. type difficulty has been experienced in securing stable reception, since the transmitting frequency may vary or drift `considerably during operation for any of a number of causes, such as change in supply voltage, thermal drift, vibration, and other effects. To receive signals from a transmitter Whose frequency thus tends to drift, it was formerly necessary to employ a receiver having a wide frequency band width to allow for drift. Such receivers are subject to the disadvantage of resulting unfavorable signal-to-noise ratio due to the increased bandwidth, A further disadvantage resides in the greater number of amplification stages required, since the gain per stage decreases with increasing band width. In superheterodyne receivers further disadvantage resides in the necess-ity for using a local oscillator, which may also be subject to drift from similar causes.

To overcome these defects, in the present system .axwlave is derived differing in frequency from the transmitted frequency by a fixed and predetermined amount. This wave is then utilized as a local oscillator frequency in a superheterodyne receiver so that the resulting intermediate frequency will be fixed and predetermined no matter what variation in transmitter frequency occurs. In this manner the transmitter frequency and local oscillator frequency are continuously maintained in the correct relation with one another,

v avoiding the above-enumerated diiculties of the prior art and permitting the use of relatively sharply tuned intermediate frequency circuits resuitlng in greatly improved operation.

According to the present invention, a single velocity-modulation oscillator-buffer tube of the type disclosed in U. S. Patent No. 2,294,942, issued September 8, 1942, in the name of Varian et al;, is utilized to simultaneously` generate a high-power ultra-high-frequency Wave suitable for;- transmission and a local oscillatorwave separated in frequency therefrom by the desired fixed intermediate frequency. Such a devicecomprises three cavity resonators successively traversed by an electron stream. The first cavity resonator serves to velocity modulate the electrons of the stream at a predetermined frequency to which the resonator is substantially tuned. These velocity-modulated electrons thereafter traverse a field-free drift space in which they become velocity-grouped or density-modulated. The vdensity-modulated stream then enters the second.

cavity -resonator which'extracts energy of the velocity-modulating frequency from the stream. Part of this extracted energy is fed back to the first resonator to sustain oscillations in the device. This portion of the system provides a selfoscillating 'ultra-high-frequency generator, and energy of this ultra-high frequency may be extracted from the second resonator for use in transmission. The electron stream is further controlled at a frequency equal to the desired intermediate frequency of the receiving system or a sub-multiple thereof. As a result of this modulation, the electron beam contains alternating current components of frequencies corresponding to the modulation side-bands of the transmitted wave as modulated by the modulating frequency. Energy at any one of these side frequencies suitable for use as the local oscillator wave may then be derived from the third cavity resonator vby tuning this cavity resonator to this local oscillator frequency.

Accordingly, it is an object of .the presentinventi-on to provide improved synchronized radio transmission and reception apparatus of the su.- perheterodyne type operating at a fixed intermediate frequency independent of the transmitted or received frequency.

It is another object of the present invention to provide improved apparatus` at ultra highfrequen-cies adapted to produce two ultra high frequency waves having frequency separations of desired amounts, independent of variation or drift Quellcy.

s,4sa,see i Y 3 l more in detail in the above-mentioned Patent No. 2,294,942. In brief, oscillator 299' comprises three cavity resonators 29|', 292 and 299'. An electron beam is projected under the influence of an accelerating voltage source 299'. successivelyV through these resonators by way of their electronpermeable walls defining gaps across which the electron beam is projected. The electrons of the beam are velocity-modulated on passing through the first gap oi resonator 29| by the oscillating electric field existing at this gap due to oscillations within the resonator 29| After passing through therleld-free drift space 299', the electrons of the beam are hunched or grouped so that they may then deliver ultra-high-frequency energy to resonator 292' upon passing through the corresponding gap of this resonator. Resonators 29| and.

292,are both tuned to a desired ultra-high-frequency f suitable for radiation ortransmission.

, Some of the energy of resonator 252' is fed back toresongtor 29| by means of the feedback line 299' to sustain the system in oscillation at this frequency f. Energy at the frequency l may then be extracted from resonator 292' by means of the coupling line 299. As thus far described. the oscillator 299 is similar to the Klystron oscillator disclosed in U. S. Patent No. 2,242,275, granted May 20, 1941, to R, H. Varian, and will produce ultra-high-frequency energy ofthe frequency ,f

in line 299. This energy is supplied t'o an antenna 294 or to any other load circuit. a

resonator, one of whose higher modes of reso-- nance has a resonant frequency equal to this output frequency f:tnf...since forsuch a resonator the selectivity is much higher than for one oscillating at its fundamental or lowest mode. However, nlter 21| may be omitted if sufficient selectivity can be obtained from resonator 292'.

The wave radiated by antenna 299 will have a portion of its energy reected from the distant object to be located, and suchv reflected energy may be received on a suitable receiving antenna indicated at 219. Antenna 219 is coupled to a mixer-219 of any suitable type. to which is also In series with the beam-accelerating voltage v :source 299 is an oscillator 299 of a-frequency which, as will be seen, determines the intermediate frequency of the superheterodyne receiver portion of the system. This oscillator 299 is illus-` tratedas having a frequencyji such as 15 megacycles per second, but may have any desired l value.

As discussed in U. S. Patent No. 2,281,935, granted May 5, 1942, to R. H. Varian and W. W. Hansen, oscillator 299 serves to phase modulate the alternating current component of the grouped electron stream so that the electron beam current represents a phase-modulated wave and will have alternating current com'- ponents of frequency ,f and of side frequencies differing from the frequency f by integral multiples of the modulating frequency fi derived from oscillator 299. Accordingly. by tuning the third resonator 299' to one of the side frequencies frnfs of the resulting modulated wave, an output may be derived from' coupling line 219 having a frequency separation with respect to the wave in line 299 equal to an integral multiple n ofthe modulating frequency fr, this multiple corresponding to the order of the side frequency to which resonator 293 is tuned, If resonator 253' is sumciently sharply selective to resonate only at this side frequency and not at the neigh- .borlng side frequencies or carrier frequency f,

a single-frequency output is derived in line 219 which is separated from the frequency f radiated from antenna 299 by the frequency f. of oscillator 299 or a desired multiple n thereof. Preferably, resonaor 259' is tuned to a higher order side frequency, for example, that corresponding fed the wave of frequency Iiinh derived from oscillator 299 and serving asa local oscillator wave in the superheterodyne receiving system. The output of mixer 219 will then be the diiference between the two input frequencies, that is nf., which represents the intermediate frequency of the system. l

This intermediate frequency may be utilized in an intermediate frequency circuit 219, one -formof which is illustrated in Fig. 22 of the above-mentioned parent application Serial No. 428,988. In this way the intermediate frequency of the receiving system is entirely independent of the frequency f; and, in fact, if the frequency f should change or drift for anyl reason, it will havev no effect upon the intermediate frequency. Accordingly, al1 of the intermediate frequency circuits may be sharply and fixedly tuned to the frequency nf. in the illustration used.

It will be noted that the intermediate frequency was chosen as a multiple nl of the modulating frequency fr of oscillator 299 and preferably twice this frequency. In this way any stray coupling between the intermediate frequency circuit 219 and oscillator 299 will be incorresponding to its rst side band and resulting in an intermediate frequency of f., harmful interaction between oscillator 299 and circuit 219 might bev encountered unless special precautions in the way of isolation and shielding are used. Such special precautions are unnecessary in the system illustrated in the figure by 'virtue of the choice of second or higher'side band for the local oscillator frequency fin.

I n the device of the present invention the output resonator 293' need not be tuned to a fixed frequency but may be provided with frequencyadjusting means of any well-known type so that it may be selectively tuned to any of a number of the side frequencies produced. In this way a single device 299' may` produce any of a number of local oscillator frequencies or any of a number of frequency separations from the frequency f,

or may provide any of a number of frequency shifts.

Although the modulator of the present invention has been illustrated as operating by varying the accelerating voltage, any other form of modulation may be used to produce the desired side frequencies. Thus, the electron beam current may be varied at the modulating frequency independently of or in conjunction with variation in the accelerating voltage, as byfimpressing the modulating voltage from oscillator 299 upon a control grid between the cathode and first resonator 25|'. Alternatively, the transit time of the electrons may be varied in any of the ways shown in Patent No. 2,281,935. It is to be understoodv that any form of-amplitude, frequency, orphase modulation, or any combination thereof, may be used, including any of those shown in Patent No. 2,281,935.

It will be seen that although the above modifications of the present invention were directed toward a radio locating system having a transmitter and a superheterodyne receiver for receiving reflected energy, in its broader aspect the present invention is concerned with the production of ultra high frequencies with Vpredetermined and fixed frequency separations which are independent of variations in the ultra high frequencies; that is, a plurality of frequencies are produced which track with one another. Also, the invention may be used as a frequency shifter or converter.

Since many changes could be made in the for velocity modulating said electron beam at a predetermined ultra high frequency, means for extracting energy of said predetermined frequency from said electron stream, means for further controllingA said electron stream in accordance with a modulating frequency, and

stream at a frequency differing from said predetermined frequency by an integral multiple of said modulating frequency.

2. Ultra high frequency apparatus, comprising means forproducing an electron stream grouped in accordance with a predetermined ultra high frequency wave, means for modulating said electron stream grouping in accordance with a modulating frequency, means for extracting energy of said predetermined frequency from said stream, and further means for extracting energy' from said stream of a frequency differing from said predetermined'frequency by an integral multiple of said modulating frequency.

3. Ultra high frequency apparatus, comprising an loscillator-buffer velocity modulation electron discharge device having three cavity resonators,

sustained oscillations at the resonant frequency of said resonators, means for extracting energy of substantially said resonant frequency from said second' resonator, means for varying the gral multiple of said modulating frequency, their difference being independent of variation of said means for further extracting energy from said the first and second of said resonators being tuned substained oscillation frequency.

4. High frequency' apparatus, comprising means for producing an electron stream, means for producing self-sustained grouping of said electron stream at a predetermined ultrahigh frequency, means for extracting energy of said frequency from said stream, means for modulating said electron grouping in accordance lwith a modulating frequency, and means for extracting energy from said stream of a frequency differing from said predetermined frequency by an integral-multiple of said modulating frequency. 5. Ultra high frequency apparatus, comprising means for producing an electron stream, means for producing self-sustained grouping of the electrons of said stream at. a predetermined frequency, means for controlling said stream at a modulating frequency, and means for extracting ultra high frequency energy from said stream at a frequency differing from said predetermined frequency by an integral multiple of said modulating frequency.

46. Apparatus as in claim 5, further including means for extracting energy of said predetermined frequency, means for radiating said ex-k tracted energy of predetermined frequency, means for receiving a portion of said 4radiated energy, and means for mixing said received energyand said different frequency extracted energy to produce an intermediate frequency of an integral multiple of said modulating fre- WILLIAM W. HANSEN. JOHN R. WOODYARD.

` REFERENCES CITED l .The following references are of record in the le' of this patent:

UNrrED s'rA'rEs PATENTS Number Name Date 1,993,395 Beers Mar. 5, 1935 2,143,864 Conklin et a1. ,12.11.17, 1939 2,189,549 Hershberger Feb. 6. 1940 Re. 21,955 Chaee Nov. 25, 1941 2,268,643 Crosby Jan. 6, 1942 2,281,935 Hansen et al. May 5, 1942 2,318,106 Ryan May 4, 1943 

